Ultrasonic delay line

ABSTRACT

An ultrasonic delay line which comprises a solid body and two input and output electro-mechanical transducers for converting electrical energy into ultrasonic mechanical energy or vice versa, and in which the ultrasonic wave, emitted from the input electro-mechanical transducer by the application of an electric input signal thereto, is reflected by at least one reflecting surface formed in the solid body and enters the output electromechanical transducer to derive therefrom an electric output signal which is delayed behind the electric input signal for a period of time during which the ultrasonic wave propagates in the solid body. The reflecting surface has at least one elliptical surface whose focuses are located each at one point on each electro-mechanical transducer or its equivalent point.

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Yokoyama Aug. 27, 1974 ULTRASONIC DELAY LINE Primary Examiner.lames W. Lawrence Assistant Examiner-Marvin Nussbaum [75] Inventor Take Yokoyama Ebma Japan Attorney, Agent, or FirmMarshall & Yeasting [73] Assignee: Mitsumi Electric Company, Limited,

Tokyo, Japan 57 ABSTRACT [22] Filed: Apr. 5, 1973 1 An ultrasonic delay lme Wl'llCh comprises a sol1d body [21] Appl' 348,114 and two input and output electro-mechanical transducers for converting electrical energy into ultrasonic [30] F i A li ti P i it D mechanical energy or vice versa, and in which the ultrasonic wave, emitted from the input electro- Apr. 6, 1972 Japan 47 33910 mechanic a1 transducer by the application of an elec 52 us. Cl. 333/30 R, 310/8 input Signal thereto i reflects? by at least one fleeting surface formed in the SOlld body and enters [51] lint. Cl. l-l03h 9/26, HOlv 7/00 [58] Field of Search 333/30 R 71, 310/8, the output electro-mechamcal transducer to derlve 310/8 1 9 4 9 7 9 8 therefrom an electric output signal which is delayed behind the electric input signal for a period of time durin which the ultrasonic wave ro a ates in the 56 n t c ted g P P g I UNITE; gg xg :DATENTS solid body. The reflecting surface has at least one elliptical surface whose focuses are located each at one Arenberg R point on each electro mechanical transducer or equivalent point.

16 Claims, 28 Drawing Figures PATENIED 3.832.655

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BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an ultrasonic delay line which comprises a solid body for propagation of ultrasonic mechanical energy therein, and two input and output electro-mechanical transducers (or a single combined input and output electro-mechanical transducer) for converting electrical energy into ultrasonic mechanical energy or vice versa, and in which the ultrasonic wave, emitted from the input electromechanical transducer (or the combined input and output electro-mechanical transducer) by the application of an electric input signal thereto, propagates in the solid body and is reflected by at least one reflecting surface formed in the solid body and enters the output electro-mechanical transducer (or the combined input and output electro-mechanical transducer) to derive therefrom an electric output signal which is delayed behind the electric input signal for a period of time during which the ultrasonic wave propagates in the solid body.

2. Description of the Prior Art In conventional ultrasonic delay lines of this type (which will be described on the assumption that they have an input and an output electromechanical transducer, for the sake of brevity), the ultrasonic wave emanating from the input electro-mechanical transducer gradually spreads as it goes away from the transducer. Consequently, the distance of propagation of the ultrasonic wave passing the center of the spreading differs from those of the ultrasonic waves deviating away from the center, so that no exactly defined delay time can be obtained between the electric input and output signals, the electric output signal becomes distorted and, further, an excellent frequency or phase characteristic cannot be obtained as a whole.

To avoid such defects experienced in the prior art, an ultrasonic delay line of the following construction has been proposed. Namely, a solid body is formed in the shape of a solid plate which has parallel, opposing first and second major surfaces, first and second transducer mounting side surfaces perpendicular to the first and second major surfaces and extending in a straight line when viewed from the sides of the first and second major surfaces, and at least one reflecting surface perpendicular to the first and second major surfaces. An input electro-mechanical transducer is mounted on the first mounting side surface and polarized parallel to the first and second major surfaces and the first mounting side surface so that the ultrasonic wave from the input electromechanical transducer may be emitted in a direction normal to the first mounting side surface as a whole. An output electro-mechanical transducer is mounted on the second transducer mounting side surface and polarized parallel to the first and second major surfaces and the second mounting side surface. The output transducer is adapted to provide a maximum electric output signal when the ultrasonic wave incident on the transducer is perpendicular to the second mounting side surface as a whole. For this purpose, it is arranged that the ultrasonic wave emitted from the input electro-mechanical transducer into the solid plate and spreading in the direction of the thickness of the solid plate is reflected by the first and second major surfaces, thereby to prevent unnecessary spreading of the ultrasonic wave in the direction of the thickness of the solid plate.

In this case, the first and second major surfaces and the reflecting surface are arranged relative to each other so that the ultrasonic wave emitted from the input electro-mechanical transducer at right angles to the first transducer mounting side surface and passing its center corresponding to the effective one of the input electro-mechanical transducer, viewed from the sides of the first and second major surfaces, is reflected at the center of the reflecting surface viewed from the sides of the first and second major surfaces and passes through the second transducer mounting side surface at its center corresponding to the effective center of the output electro-mechanical transducer viewed from the sides of the first and second major surfaces and perpendicularly to the mounting side surface and then strikes the output electro-mechanical transducer. Further, there are provided on the first and second major surfaces ultrasonic wave absorbing members which are spaced a predetermined distance apart from and extend parallel to the center of the path of the ultrasonic wave which emanates from the input electromechanical transducer and gradually spreads as it goes away therefrom. Accordingly, those ultrasonic waves which have spread in the direction of the surface dimension of the solid plate are absorbed by the ultrasonic wave absorbing members, thereby preventing that the ultrasonic waves having unnecessarily spread out from the path in the direction of the surface dimension of the solid plate strike the output electromechanical transducer.

In such a conventional ultrasonic delay line, however, since the ultrasonic wave spreading out in the direction of the surface dimension of the solid plate is absorbed by the absorbing members, only one part of the ultrasonic wave emitted from the input electromechanical transducer reaches the output electromechanical transducer, and accordingly the resulting transmission loss between the electric input and output signals is appreciably great. Further, the use of the ultrasonic wave absorbing members naturally necessitates a process for mounting them on the first and second major surfaces of the solid plate. Moreover, in addition to the ultrasonic wave passing the center of the ultrasonic wave path, the ultrasonic wave spreading between the center of the path and the inner side of the ultrasonic wave absorbing member disposed close to the output electro-mechanical transducer enters the output transducer, so that an exactly defined delay time cannot be obtained, the electric output signal is distorted and an excellent frequency or phase characteristic cannot be obtained.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is to provide an ultrasonic delay line which is designed so that even if the ultrasonic wave emitted from an input electro-mechanical transducer (or a combined input and output electro-mechanical transducer) spreads as it goes away therefrom, an exactly defined delay time can be omitted between electric input and output signals, the electric output signal does not become distorted and an excellent frequency or phase characteristic can be obtained.

Another object of this invention is to provide an ultrasonic delay line which employs a solid plate as in the conventional ultrasonic delay line but provides the abovementioned excellent features without mounting any ultrasonic wave absorbing members on the solid plate and which is small in transmission loss between electric input and output signals.

Other objects, features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are plan and front views respectively illustrating one example of an ultrasonic delay line according to this invention;

FIGS. 2 to 9 respectively show other examples of this invention;

FIGS. 10 to 18 respectively show other examples of this invention;

FIGS. 19A and 19B are plan and front views illustrating another example of this invention; and

FIGS. 20 to 26 respectively illustrate other examples of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a first embodiment of this invention, which comprises a solid plate 1 for propagation of ultrasonic mechanical energy therethrough and input and output electro-mechanical transducers 2 and 2' for converting electrical energy into ultrasonic mechanical energy or vice versa.

The solid plate 1 may be formed of, for example, glass, elinvar, ceramics or like known material. The solid plate 1 has parallel, opposing first and second major surfaces 3a and 3b, first and second transducer mounting side surfaces 4 and 4 normal to the major surfaces 3a and 3b and extending in a straight line when viewed from the sides of the major surfaces, and a reflecting surface D normal to the major surfaces 3a and 3b. In this case, the distance between the first and second major surfaces 3a and 3b, that is, the thickness of the solid plate 1 is selected as relatively small as 0.5 to 5 times the wavelength of the ultrasonic wave emanating from the input electro-mechanical transducer 2, as will be described hereinbelow. The reason why the thickness of the solid plate 1 is selected to be 0.5 to 5 times the wavelength of the ultrasonic wave is that when it is less than 0.5 times, the mechanical strength of the solid plate 1 is insufficient and that when it is less than 5 times, even if the ultrasonic wave slightly spreads in the thickness dimension of the plate, it is immediately reflected by the first and second major surface 3a and 3b and is thereby caused to propagate in the solid plate 1 substantially parallel to the major surfaces 3a and 3b.

The transducers 2 and 2' may be any known ones but have the shape of a plate as a whole and they are respectively mounted on the transducer mounting side surfaces 4 and 4' through an adhesive binder, though not shown. In this case, the transducer 2 is polarized parallel to the major surfaces 3a and 3b and the mounting side surface 4, while the transducer 2' is similarly polarized parallel to the major surfaces 3a and 3b and the mounting side surface 4'. These transduces 2 and 2' are of such a size that the ultrasonic wave emanating from the transducers can be equivalently obtained from the centers on the mounting side surfaces corresponding to the effective centers of the transducers viewed from the sides of the major surfaces 3a and 3b. Consequently, the ultrasonic wave, which is emitted from the central point P on the mounting side surface 4 viewed from the sides of the major surfaces 3a and 3b, corresponding to the effective central point on the transducer 4, by the application of an electric input signal to the transducer 4 through an input terminal (not shown) led out therefrom, gradually spreads as it goes away from the point P but, as a whole, it is effectively emitted perpendicular to the side surface 4. While, an electric output signal, which is derived from an output terminal (not shown) led out from the transducer 2', becomes maximum when the ultrasonic wave enters, perpendicular to the side surface 4', the central point P on the side surface 4 viewed from the sides of the major surfaces 3a and 3b, corresponding to the effective central point on the transducer 2.

The aforementioned transducer mounting side surfaces 4 and 4 and the reflecting surface D are arranged relative to each other in such a manner that the ultrasonic wave, emitted from the transducer 2 at the point P perpendicularly to the side surface 4, propagates in the solid plate 1 and is reflected at the central point P on the reflecting surface D viewed from the sides of the major surfaces 3a and 3b and enters the transducer 2' at the point P perpendicularly to the side surface 4'. The ultrasonic wave passing the line joining P P and P will hereinafter be referred to as a central ultrasonic wave and indicated by 5P. In this case, the reflecting surface D is opposed to the transducer mounting side surfaces 4 and 4 and lies in a plane extending along an elliptic line passing the point P with the points P and P being used as focuses, when viewed from the major surfaces 3a and 3b.

With such an arrangement as described above, the ultrasonic wave emitted from the transducer 2 at the point P towards the reflecting surface D and spreading in the direction of thickness of the solid plate 1 is reflected by the major surfaces 3a and 3b and it is regarded as substantially parallel to the major surfaces 3a and 3b, since the solid plate 1 is relatively thin. On the other hand, the ultrasonic waves, which spread along maximum spreading paths 5a and 5b on both sides of the central ultrasonic wave path 5? as they go away from the point P are reflected at point a and b on the reflecting surface D on both sides of the point P respectively. In this case, the points a and b lie on the elliptic line passing the point P, with the points P and P being used as focuses, so that the path 5a connects the points P a and P and hence becomes complete, while the path 5b connects the points P b and P and hence similarly becomes complete. The paths 5a and 5b are equal in length to that 5P.

Accordingly, if the eccentricity of the above elliptic line is predetermined in accordance with a desired delay time of the electric output relative to the electric input signal, substantially almost all of the ultrasonic wave emitted from the input transducer 2 strikes the output transducer 2, even if it spreads as it goes away from the transducer 2, so that it is possible to obtain the function of an ultrasonic delay line which is small in transmission loss between the electric input and output signals. Of course, all the ultrasonic paths to the transducer 2' are equal in length, so that an exactly defined delay time can be obtained, the electric output signal does not become distorted and an excellent frequency or phase characteristic can be obtained as a whole.

FIG. 2 shows a second embodiment of this invention, in which parts corresponding to those in FIG. 1 are marked with the same reference numerals and characters. The reflecting surface is composed of two surfaces D and D The transducer mounting side surfaces 4 and 4' and the reflecting surfaces D and D are disposed relative to each other in such a manner that the ultrasonic wave emitted from the input transducer 2 at the point P perpendicularly to the side surface 4 propagates in the solid plate 1 and is reflected at the central point F on the reflecting surface D, and then reflected at the central point P on the reflecting surface D and strikes the output transducer 2' at the point P In this case, the reflecting surface D is a straight line surface which extends along a straight line passing the point P and extending normal to a bisector of an angle formed between a line connecting the points P, and P and that connecting the points P and P On the other hand, the reflecting surface D is opposed to the side surface 4 and the reflecting surface D and it is an elliptic surface which, if an equivalent central point P 1 symmetrical with the point P with respect to an imaginary plane M including the surface D is considered, extends along an elliptic line using the points P and P -1 as focuses and passing the point P With the above construction of the second embodi ment, the path 5? of the ultrasonic wave emanating from the input transducer 2 connects the points P P P and P and becomes complete, while the paths 5a and 5b respectively connect P points a and b, on the reflecting surface D on both sides of the point P points a and b on the reflecting surface D on both sides of the point P and the point P and become complete, because the points a, and b, on the reflecting surface D, lie on the elliptic line using as its focuses the points P and P -1 equivalent to the point P and passing the point P and because the point a and b on the reflecting surface D lie on the straight line including the point P and extending perpendicular to the bisector of the angle between the line connecting the points P and P and that connecting the points P and P The paths 5a and 5b are equal in length to that 5?. Accordingly, it is possible to obtain the same excellent results as those obtainable with the enbodiment of FIG.

FIG. 3 illustrates a third embodiment of this invention, in which parts corresponding to those in FIG. 2 are identified by the same reference numerals and characters and no detailed description will be repeated. This embodiment is identical in construction with that of FIG. 2 except that the transducer mounting side surfaces 4 and 4 and the reflecting surfaces D and D are arranged relative to another in such a manner that the ultrasonic wave may cross itself in the solid plate 1. This embodiment provides the same results as those 0btainable with the embodiment of FIG. 2 and a long delay time.

FIG. 4 shows a fourth embodiment of this invention, in which parts corresponding to those in FIG. 1 are designated by the same reference numerals and characters and of which no detailed description will be given. This embodiment employs three reflecting surfaces D D and D The transducer mounting side surfaces 4 and 4 and the reflecting surfaces D to D are positioned relative to one another such that the ultrasonic wave, emitted from the output transducer 2 at the point P perpendicularly to the side surface 4, is successively reflected at the central pointsP P and P; on the reflecting surfaces D D and D before striking the output transducer 2 at the point P perpendicular to the side surface 4. In this case, the reflecting surface D is a surface extending along a straight line including the point P and normal to the bisector of the angle between a line connecting the points P and P and that connecting the points P and P The reflecting surface D is a surface extending along a straight line including the point P and extending perpendicular to the bisector of the angle between a line connecting the points P and P and that connecting the points P and P On the other hand, the reflecting surface D is a surface that includes an elliptic line including the point P and using as its focuses an equivalent central point P -l symmetrical with the point P with respect to an imaginary plane M, including the surface D and an equivalent central point P -1 symmetrical with the point P with respect to an imaginary plane M including the surface D With such an arrangement as described above, the same results as those obtainable with the foregoing examples can be obtained, as will be seen from the foregoing, so that no detailed description will be made in this connection. The path 5? is formed with straight lines connecting the points P P P P and P the path 5a is formed with straight lines interconnecting the points P a a and a on the reflecting surfaces D D and D and P the path 5b is formed with straight lines interconnecting the points P b b and a on the reflecting surfaces D D and D and P and the paths 5a and 5b are equal in length to the path 5P, so that it is possible to obtain the same results as those obtainable with the foregoing embodiments.

FIG. 5 shows a modified form of the ultrasonic delay line of FIG. 4 which is identical in construction with that of FIG. 4 except that the transducers 4 and 4' and the reflecting surfaces D to D are positioned relative to one another so that the ultrasonic wave may cross itself in the solid plate 1. Hence, no detailed description will be repeated but this embodiment provides the same results as those obtainable with the embodiment of FIG. 4 and a long delay time.

FIG. 6 illustrates another modification of the ultrasonic delay lines of FIGS. 4 and 5, which is identical in construction with the latter except that the reflecting surface D lies in a plane extending along a straight line passing the point P and extending perpendicular to the bisector of the angle between a line connecting the points P and P and that connecting the points P and P that the reflecting surface D lies in a plane extending along a straight line passing the point P and extending perpendicular to the bisector of the angle between a line connecting the points P and P and that connecting the points P and P and that the reflecting surface D extends along an elliptic line whose focuses, if an equivalent point P l and an imaginary plane M l symmetrical with the point P and the reflecting surface D, with respect to an imaginary plane M including the surface D and an equivalent point P '-2 symmetrical with the point P '2 with respect to the imaginary plane M 1 are considered, are selected at the point P and the point P -2 and which passes the point P This embodiment also provides the same results as those obtainable with the embodiments of FIGS. 4 and 5.

FIG. 7 shows a seventh embodiment of this invention which employs four reflecting surfaces D to D and in which the reflecting surface D is similar to that D employed, for example, in the embodiment of FIG. 4, the reflecting surfaces D and D are similar to those D and D used in the embodiment of FIG. 6 and the reflecting surface D extends along an elliptic line whose focuses are at an equivalent central point P 1 similar to that in FIG. 4 and an equivalent central point P 2 similar to that in FIG. 6 and which passes the point P Accordingly, this embodiment also'provides the same results as those obtainable with the foregoing embodiments.

FIG. 8 illustrates a modified form of the ultrasonic delay line of FIG. 7, which is identical in construction therewith except that the transducer mounting side surface and the reflecting surfaces are so arranged that the ultrasonic wave may cross itself in the solid plate. This embodiment also provides the same results as those obtainable with the foregoing embodiment.

FIG. 9 shows a ninth embodiment of this invention which employs five reflecting surfaces D to D In this embodiment, the reflecting surfaces D D D and D are formed to lie in planes extending straight lines in the manners described previously and the surface D is formed to lie extends along an elliptic line in the manner described above. The same results as those obtainable with the foregoing embodiments can be obtained. Further, the number of the reflecting surfaces is odd as in the embodiment of FIG. 5 and if that number is taken as n, the [(n l)/2]th surface from the side of the side surface 4, that is, the intermediate surface, is elliptic, so that the reflecting surfaces can be positioned symmetrical with respect to a line normal to that connecting the transducers 2 and 2'. This facilitates the fabrication of the ultrasonic delay line and provides a long delay time.

FIG. 10 illustrates a tenth embodiment of this invention which corresponds to the foregoing first one and in which parts corresponding to those in FIG. 1 are indicated by the same reference numerals and characters and of which no detailed description will be given. In this embodiment, the transducer 2 and 2 are each of such a size that the ultrasonic wave is emitted from the transducer 2 or 2' to the full width between both side points on the mounting side surface 4 or 4 corresponding to effective side points of the transducer, viewed from the major surfaces 3a and 3b. Consequently, the ultrasonic wave, which is emitted from the area on the side surface 4 between the side points a and b corresponding to the effective ones of the transducer 2, gradually spreads as it goes away from the areas defined between the both side points 0 and b The transducer mounting side surfaces 4 and 4 and the reflecting surface D are arranged relative to one another so that the ultrasonic waves, emitted from the transducer 2 and passing the points P a and b perpendicularly to the side surface 4, are respectively reflected at the central point P and points c and d on the both sides thereof on the reflecting surface D viewed from the major surfaces 3a and 3b, and enter the output transducer 2 passing through the point P and those a and b on the both sides thereof perpendicularly to the side surface 4' and that the respective ultrasonic wave paths indicated by 5F, 50 and 5d may be equal in length to one another. Further, the reflecting surface D comprises a linear area a extending along a straight line connecting points 0 and d, and first and second elliptic areas d,, and d continuously extending outwardly of the linear area d on the both sides thereof respectively. In this case, the linear area-d lies in plane extending along the straight line connecting the points 0 and d, when viewed from the major surfaces 3a and 3b but this straight line passes the point P since the path passing the points P P and P is equal in length to those passing a c and a and 12 d, and b The elliptic area d extends along an elliptic line whose focuses are selected at the points a and a when viewed from the sides of the major surfaces 3a and 3b. While, the elliptic area d extends along an elliptic line whose focuses are selected at the points b and b With such an arrangement as described above, the ultrasonic wave emitted from the transducer 2 through the area between the points a and b towards the reflecting surface D, and spreading in the direction of thickness of the solid plate 1 is reflected by the major surfaces 3a and 3b as in the case of FIG. 1, so that it is regarded as substantially parallel to the major surfaces 3a and 3b. On the other hand, the ultrasonic waves, which spread along maximum spreading paths 5a and 5b outwardly of the ultrasonic wave paths 5c and 5d are reflected at outer points al and b on the elliptic areas a and a' of the reflecting surface D respectively. In this case, the point a lies on the elliptic line whose focuses are at the points a and a and which passes the point a and the points [9, lies on the elliptic line whose focuses are at the points h and b and which passes the point b so that the path 5a connects the points a a and a and hence becomes complete, while the path 5b connects the points a b and a and hence similarly becomes complete. The paths 5a and 5b are equal in length to those SP, 50 and 5d.

Accordingly, it is possible to obtain the function of delay means which provides an exactly defined delay time and an excellent characteristic.

FIG. 11 shows an eleventh embodiment of this invention, in which parts corresponding to those in FIG. 10 are marked with the same reference numerals and characters. The reflecting surface is composed of two surfaces D and D The transducer mounting side surfaces 4 and 4' and the reflecting surfaces D and D are disposed relative to each other in such a manner that the ultrasonic waves emitted from the input transducer 2 at the points P a and b perpendicularly to the side surface 4 propagates in the solid plate 1 along the paths 5P, 5c and 5d of the same length and are reflected at the points P 0 and d, on the reflecting surface D and then reflected again at the points P c and d on the reflecting surface D and strike the output transducer 2 at the points P a and b perpendicularly to the side surface 4. In this case, the reflecting surface D is a straight line surface which extends along a straight line passing the points P 0 and 11 and extending normal to a bisector of an angle formed between a line connecting the points P and P and that connecting the points P and P On the other hand, the reflecting surface D is opposed to the side surface 4 and the reflecting surface D and it is an elliptic surface comprising a straight-line area a connecting the points 0 and d and elliptic areas (1,, and d extending outwardly of the area d,,. The elliptic areas d extends along an elliptic line whose focuses, if equivalent points P '-l, a 1 and D, are considered, are selected at the points a and a '1 and which starts from the point 0 The elliptic area d extends along an elliptic line whose focuses are I at the points h and b "-1 and which starts from the point d With the above construction of the eleventh embodi- This embodiment is identical in construction with that of FIG. 11 except that the transducer mounting side surfaces 4 and 4 and the reflecting surfaces D and D are arranged relative to one another in such a-manner 7 that the ultrasonic wave may cross itself in the solid plate 1. This embodiment provides the same results as those obtainable with the embodiment of FIG. 11 and a long delay time. I

FIG. 13 shows a thirteenth embodiment of this invention, in which parts correspondingto those in FIG. 10 are designated by the same reference numerals and characters and of which no detailed description will be given. This embodiment employs three reflecting surfaces D D and D The reflecting surfaces D and D lie in planes extending along straight lines and thereflecting surface D comprises a straight-line area zi and elliptic areas d and d I With such an arrangement as described above, the same results as those obtainable with the foregoing examples can be obtained, as will be seen from the foregoing, so that no detailed description will be made in this connection.

FIG. 14 shows a modified form of the ultrasonic delay line of FIG. 13 which is identical in construction with that of FIG. 13 exceptthat the transducers 4 and 4 and the reflecting surfaces D and D are positioned relative to one another so that the ultrasonic wave may cross itself in the solid plate 1. Hence, no detailed description will be repeated but this embodiment provides the same results as those obtainable with the embodiment of FIG. 13 and a long delay time.

FIG. 15 illustrates another modification of the ultra sonic delay lines of FIGS. 13 and 14, which is identical in construction with the latter except that the reflecting surfaces D and D respectively lie in planes extending along straight lines and that the reflecting surface D comprises a straight-line area and an elliptic area. This embodiment alsoprovides the same results as those obtainable with the embodiments of FIGS. 13 and 14.

FIG. 16 shows a sixteenth embodiment of the invention which employs four reflecting surfaces D to D and in which the reflecting surfaces D and D are straight and the reflecting surface D comprises a straight-line area and an elliptic area. This embodiment also provides the same results as those obtainable with the foregoing embodiments.

FIG. 17 illustrates a modified form of the ultrasonic delay line of FIG. 16, which is identical in construction therewith except that the transducer mounting side surfaces andthe reflecting surfaces are so arranged that case, since the points a and b lie on an elliptic line 10 the ultrasonic wavemay cross itself in the'solid plate. This embodiment also provides the same results as those obtainable with the foregoing embodiment.

FIG.'18 shows an eighteenth embodiment of this invention which employs five reflecting surfacesD, toD In this embodiment, the reflecting surfaces D D D and D5 are formed to lie-in planes extending straight linesin the manners described previously and the surface D is formed to comprise a straight-line area and an elliptic area in the manner described above. The same results as those obtainable with the foregoing embodiments can be obtained. Further, the number of the reflecting surfaces is odd as in the embodiment of FIG. 14, so that the reflecting surfaces can, be positioned symmetrical with respect to a line normal to that connecting the transducers land 2 as described previously with regard to FIG. 9. This facilitates'the fabrica-. tion of the ultrasonic delay line and provides a long delay time. v

FIG. l9'shows another embodiment of thisinvention, which has three reflecting surfaces D D and D, as in the foregoing embodiment of FIGS, in which parts corresponding to those in FIG. 5 are identified by the same reference numerals and characters and of which no detailed description will be given. In the present embodiment, the reflecting surface D lies in a linear plane extending across the central point P: on the reflecting surface D when viewed from the sides of the major surfaces 3a and 3b; the reflecting surface D extends along an elliptic line whose focuses are selected at the central points P and P and which extends across the central point P when viewed from the sides of the major-surfaces 3a and 3b; and the reflecting surface D extends along an elliptic line .whose focuses are similarly selected at the central points P and P and which extends across the central point P With the above construction of the nineteenth embodiment, the ultrasonic wave emitted from the transducer 2 at the point P towards the reflecting surface D and spreading in the direction of the thickness of the solid plate 1 is reflected by the major surfaces 3a and 3bas in the foregoing examples and it is regarded as substantially parallel to the major surfaces 3a and 3b. On the other'hand, the ultrasonic waves, which spread along maximum spreading paths 5a and 5b on both sides of the central ultrasonic wave path 5P as they go away from the point P are reflected at points a and b, on the reflecting surface D on both sides of the point P respectively. In this case, the points a, and b lie on the elliptic line whose focuses are at the points P and P and which passes the point P,, so that the ultrasonic waves are reflected atthe reflecting surface D and both centered on the point P and reflected at this point. Then, the ultrasonic waves thus reflected at the point P are reflected again at points a and b on the reflecting surfaceD on both sides of a point P In this whose focuses are selected at the points P and P and which passes the point P the ultrasonic waves thus reflected at the reflecting surfaces D are both centered on the point P This embodiment is small in transmission loss and capable of providing an exactly defined delay. time and excellent characteristics, as is the case with the foregoing embodiments.

FIG. 20 shows a twentieth embodiment of this invention, in which parts corresponding to those in FIG. 19 are identified by the same reference numerals and characters and no detailed description will be repeated. This embodiment has four reflecting surfaces D to D The reflecting surface D extends along an elliptic line whose focuses are selected at the points P and P and which passes the point P the reflecting surfaces D and D lie in planes extending along straight lines; and the reflecting surface D extends along an elliptic line whose focuses are at the point P 1 and P and which passes a point P With such an arrangement of the twentieth embodiment, it is possible to obtain the same excellent results as those obtainable with the embodiment of FIG. 19.

FIG. 21 illustrates a twenty-first embodiment of this invention which employs five reflecting surfaces D to D In the present embodiment, the reflecting surfaces D D and D lie in planes extending along straight lines and those D and D extend along elliptic lines. This embodiment also provides the same results as those obtainable with the foregoing examples.

FIG. 22 shows a twenty-second embodiment of this invention in which three linear reflecting surfaces D D and D and elliptic ones D and D are sequentially arranged in order of D D D from the side of the input transducer 2. This embodiment, though not described in detail, also provides the same results as those obtainable with the foregoing examples.

FIG. 23 illustrates another embodiment of this invention which employs four linear reflecting surfaces D D D. and D and two elliptic reflecting surfaces D and D This embodiment, though not described in detail, also provides the same results as those obtainable with the foregoing examples.

FIG. 24 shows another embodiment of this invention employing two linear reflecting surfaces D and D and three elliptic reflecting surfaces D D and D FIG. 25 another embodiment employing four linear reflecting surfaces D,, D D and D and three elliptic reflecting surfaces D D and D and FIG. 26 another embodiment employing five linear reflecting surfaces D D D D and D and four elliptic reflecting surfaces D D D-, and D Though not described in detail, these embodiments also provide the same results as those obtainable with the foregoing examples.-

Where more than three reflecting surfaces are provided as in the embodiments of FIGS. 19 to 26, if the number of the reflecting surfaces is taken as n and if the reflecting surfaces are sequentially taken as D D D the reflecting surfaces (taken as D D D except qs ones (q being an integer greater than 3) sequentially selected from the reflecting surfaces D to D, are each formed straight (in the case of n 3, such straight-line surface is not present) and the reflecting surfaces D D D are also straight-line surfaces respectively. If the central point on the mounting side surface 4 is taken as g if the central points on the reflecting surfaces D D g, D are taken as g g 3,, respectively and if the central point on the mounting side surface 4 is taken as g 1), the reflecting sur face D (1' l, 3, ...q) extends along an elliptic line whose focuses are at the central point g or its equivalent point and the central point g or its equivalent point when viewed from the central point g,.

The foregoing description has been made in connection with the case where the solid plate 1 has two transducer mounting side surfaces 4 and 4' and input and output electro-mechanical transducers 2 and 2' are mounted thereon. This is limited to the case where the ultrasonic wave is regarded as being emitted from the effective central point of the input transducer 2 as in the embodiments of FIGS. 1 to 9 and 19 to 26 but it also possible to use the transducer mounting side surface 4 as a reflecting surface and cause the transducer on the mounting side surface 4 to serve as a combined input and output transducer, by which the resulting.

delay time can be lengthened twice that obtainable with the foregoing embodiment and the same results as those described in the foregoing can be obtained.

The foregoing embodiments should be construed as merely illustrative of this invention and many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.

What is claimed is:

1. An ultrasonic delay line comprising:

a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and

b. first and second electro-mechanical transducers for converting electrical energy into ultrasonic mechanical energy or vice versa,

c. the solid plate having parallel, opposing first and second major surfaces, first and second transducer mounting side surfaces normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D to D (n being an integer) normal to the first and second major surfaces,

i. the first electro-mechanical transducer being mounted on the first transducer mounting side surface and polarized parallel to the first and second major surfaces and the first mounting side surface,

ii. the second electro-mechanical transducer being mounted on the second transducer mounting side surface and polarized parallel to the first and second major surfaces and the second mounting side surface,

e. the first and second mounting side surfaces and the reflecting surfaces D to D being arranged relative to one other in such a manner that the ultrasonic wave, emitted from the first electro-mechanical transducer and normal to the central point on the first mounting side surface corresponding to the effective central point on the first electro-mechanical transducer viewed from the sides. of the first and second major surfaces, propagates in the solid plate and is successively reflected at central points P P P on the reflecting surfaces D D D viewed from the sides of the first and second major surfaces and strikes the second electro-mechanical transducer normal to the second mounting side surface corresponding to the effective central point on the second electro-mechanical transducer, viewed from the sides of the first and second major surfaces,

i. each of the reflecting surfaces D to D except one of them D lying in a plane extending along a straight line passing the central point on that reflecting surface viewed from the sides of the first and second major surfaces (in the case of n 1, any of such reflecting surfaces being not present), and

ii. said reflecting surface D extending along a elliptic line whose focuses are effectively located at the central points on the first and second mounting side surfaces viewed from the central point of the elliptic reflecting surface D viewed from the sides of the first and second major surfaces or at equivalent central points to them and which passes the central point on the said elliptic reflecting surface D to focus the ultrasonic wave from one transducer onto the other transducer.

2. An ultrasonic delay line comprising:

a. a solid plate propagation of ultrasonic mechanical energy therethrough, and

b. an electro-mechanical transducer for converting electrical energy into ultrasonic mechanical energy or vice versa,

c. the solid plate having parallel, opposing first and second major surfaces, a transducer mounting side surface normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D to D normal to the first and second major surfaces,

d. the electro-mechanical transducer being mounted on the transducer mounting side surface and polarized parallel to the first and second major surfaces and the mounting side surface,

e. the mounting side surface and the reflecting surfaces D to D, being arranged relative to one other in such a manner that the ultrasonic wave, emitted from the first electro-mechanical transducer normal to the first mounting side surface corresponding to the effective central point on the electromechanical transducer viewed from the sides of the first and second major surfaces, propagates in the solid plate and is successively reflected at central points P P P, on the reflecting surfaces D D D viewed from the sides of the first and second major surfaces and then successively reflected again at the central points P,, P,, P, on the reflecting surfaces D,, D,, D and strike the electro-mechanical transducer,

i. each of the reflecting surfaces D to D except one of them D lying in a plane extending along a straight line passing the central point on that reflecting surface viewed from the sides of the first and second major surfaces, and

ii. said reflecting surface D extending along an elliptic line whose focuses are selected at the central points on the mounting side surface and reflecting surface D viewed from the central point on the reflecting surface D viewed from the sides of the first and second major surfaces or at equivalent central points to them and which passes the central point on the reflecting surface 'D 3. An ultrasonic delay line comprising:

a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and

b. first and second electro-mechanical transducers for converting electrical energy into ultrasonic mechanical energy or vice versa,

0. the solid plate having parallel, opposing first and second major surfaces, first and second transducer mounting side surfaces normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D to D normal to the first and second major surfaces,

i. the first electro-mechanical transducer being mounted on the first transducer mounting side surface and polarized parallel to the first and second major surfaces and the first mounting side surface,

ii. the second electro-mechanical transducer being mounted on the second transducer mounting side surface and polarized parallel to the first and second major surfaces and the second mounting side surface,

. the first and second mounting side surfaces and the reflecting surfaces D to D being arranged relative to one other in such a manner that the ultrasonic waves, emitted from the first electro-mechanical transducer normal to the central and first and second side points on the first mounting side surface corresponding to the effective central and both side points on the first electro-mechanical transducer viewed from the sides of the first and second major surfaces, respectively propagate in the solid plate along paths of the same length and are successively reflected at central points P P P,, and first and second side points c and d 0 and d 0,, and d on the both sides thereof on the reflecting surfaces D D D viewed from the sides of the first and second major surfaces and strike the second electro-mechanical transducer perpendicularly passing the central point and first and second side points on the second mounting side surface respectively corresponding to the effective central and both side points on the second electromechanical transducer, viewed from the sides of the first and second major surfaces,

i. each of the reflecting surfaces D to D except one of them D lying in a plane extending along a straight line passing the central point on that reflecting surface viewed from the sides of the first and second major surface (in the case of n 1, any of such reflecting surfaces being not present),

ii. said reflecting surface D comprising a linear surface area extending along a straight line connecting the first and second side points on the reflecting surface and first and second elliptic surface areas continuously extending outwardly of the linear surface area, viewed from the sides of the first and second major surfaces,

iii. the first elliptic surface area extending along a first elliptic line whose focuses are at the first side points on the first and second mounting side surfaces viewed from the first side point on the linear surface area or their equivalent side poitns and which starts from the first side point on the linear surface area, and

iv. the second elliptic surface area lying in a plane extending along a second elliptic line whose focuses are at the second side points on the first and second mounting side surfaces viewed from the second side point on the linear surface area or their equivalent side points and which starts from the second side point on the linear surface area.

4. An ultrasonic delay line comprising:

a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and

b. an electro-mechanical transducer for convening electrical energy into ultrasonic mechanical energy or vice versa,

c. the solid plate having parallel, opposing first and second major surfaces, a transducer mounting side surface normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D to D normal to the first and second major surfaces,

d. the electro-mechanical transducer being mounted on the the transducer mounting side surface and polarized parallel to the first and second major surfaces and the mounting side surface,

e. the mounting side surface and the reflecting surfaces D, to B, being arranged relative to one other in such a manner that the ultrasonic waves, emitted from the first electro-mechanical transducer normal to the central and first and second side points on the first mounting side surface respectively corresponding to the effective central and both side points on the electro-mechanical transducer viewed from the sides of the first and second major surfaces, respectively propagates in the solid plate along paths of the same length and are successively reflected at central points P P P, and first and second side points 0, and d c and d c and d,, on the both sides thereof on the reflecting surfaces D D D, viewed from the sides of the first and second major surfaces and then successively reflected again at the central points P,, P,, P and the first and second side points c,, and d 0,.- and d,, c and d respectively on the both sides thereof and strike the electro-mechanical transducer,

i. each of thereflecting surfaces D to D except one of them lying in a plane extending along a straight line passing the central point on that reflecting surface viewed from the sides of the first and second major surfaces ii. the reflecting surface D comprising a linear surface area extending along a straight line connecting the first and second side points on the reflecting surfaces and first and second elliptic surface areas continuously extending outwardly of the linear surface area, viewed from the sides of the first and second major surfaces,

iii. the first elliptic surface area extending along a first elliptic line whose focuses are at the first side points on the first and second mounting side surfaces viewed from the first side points on the linear surface area or their equivalent side points and which starts from the first side point on the linear surface area, and

iv. the second elliptic surface area extending along a second elliptic line whose focuses are at the second side points on the first and second mounting side surfaces viewed from the second side point on the linear surface area or their equivalent side points and which starts from the second side point on the linear surface area.

5. An ultrasonic delay line. comprising:

a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and

b. first and second electro-mechanical transducers for converting electrical energy into ultrasonic mechanical energy or vice versa,

c. the solid plate having parallel, opposing first and second major surfaces, first and second transducer mounting side surfaces normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D to D normal to the first and second major surfaces,

i. the first electro-mechanical transducer being mounted on the first transducer mounting side surface and polarized parallel to the first and second major surfaces and the first mounting side surface,

ii. the second electro-mechanical transducer being mounted on the second transducer mounting side surface and polarized parallel to the first and second major surfaces and the second mounting side surface,

e. the first and second mounting side surfaces and the reflecting surfaces D to D being arranged relative to one other in such a manner that the ultrasonic wave, emitted from the first electro-mechanical transducer and normal to the central point on the first mounting side surface corresponding to the effective central point on the first electro-mechanical transducer viewed from the sides of the first and second major surfaces, propagates in the solid plate and is successively reflected at central points P P P on the reflecting surfaces D D D viewed from the sides of the first and second major surfaces and strikes the second electro-mechanical transducer perpendicularly passing the central point on the second mounting side surface corresponding to the effective central point on the second electro-mechanical transducer, viewed from the sides of the irst and second major surfaces,

i. each of the reflecting surfaces except q reflecting surfaces D D g, B respectively sequentially selected from those D to D lying in a plane extending along a straight line passing the central point on that reflecting surface, viewed from the sides of the first and second major surfaces (in the case of n q, such linear reflecting surfaces are not present),

ii. each of the reflecting surfaces D g, D D lying in a plane extending along a straight line passing the central point on that reflecting surface, viewed from the sides of the first and second major surfaces, and

iii. the reflecting surface D (i l, 3, q), if the central point on the mounting side surface is taken as if the central points on the reflecting surfaces D D D are taken as g g g, respectively and if the central point on the second mounting side surface is taken as g lying in a plane extending along an elliptic line whose focuses are at the central points g and g viewed from the central point g, viewed from the sides of the first and second major surfaces and which passes the central point g,.

6. An ultrasonic delay line comprising:

a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and I b. an electro-mechanical tranducer for converting electrical energy into ultrasonic mechanical energy or vice versa,

c. the solid plate having parallel, opposing first and second major surfaces, a transducer mounting side surface normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D to D normal to the first and second major surfaces,

d. the electro-mechanical transducer being mounted on the transducer mounting side surface and polarized parallel to the first and second major surfaces and the mounting side surface,

e. the mounting side surface and the reflecting surfaces D, to D, being arranged relative to one other in such a manner that the ultrasonic wave, emitted from the electro-mechanical transducer normal to the central point on the mounting side surface corresponding to the effective central point on the electro-mechanical transducer viewed from the sides of the first and second major surfaces, propagates in the solid plate and is successively reflected at central points P P P on the reflecting surfaces D D D viewed from the sides of the first and second major surfaces and then successively reflected again at the central points P,, P,, P, on the reflecting surfaces D,, D,, D and strikes the electro-mechanical transducer,

i. each of the reflecting surfaces except q reflecting surfaces (taken as D D D respectively sequentially selected from those D, to D,, lying in a plane extending along a straight line passing the central point on the reflecting surface, viewed from the sides of the first and second major surfaces,

ii. each of the reflecting surfaces D D D lying in a plane extending along a straight line passing the central point on that reflecting surface, viewed from the sides 'of the first and second major surfaces, and I iii. the reflecting surface D (i l, 3, q), if the central point on the mounting side surface is taken as g if the central points on the reflecting surfaces D D D are taken as g g g, respectively and if the central point P on the reflecting surface is taken as g extending along an elliptic line whose focuses are at the central points g,., and g viewed from the central point g, viewed from the sides of the first and second major surfaces and which passes the central point '81- 7. An ultrasonic 'delay line according to claim 1 wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.

8. An ultrasonic delay line according to claim 2, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wave length of the ultrasonic mechanical energy wave.

9. An ultrasonic delay line according to claim 3, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.

10. An ultrasonic delay line according to claim 4, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.

11. An ultrasonic delay line according to claim 5, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.

12. An ultrasonic delay line according to claim 6, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.

13. An ultrasonic delay line according to claim 1 wherein the value n is an odd number larger than 3 and the elliptic reflecting surface is n H2 th from the first transducer mounting side surface.

14. An ultrasonic delay line according to claim 2, wherein the value n is an odd number larger than 3 and the elliptic reflecting surface is n l/2 th from the first transducer mounting side surface.

15. An ultrasonic delay line according to claim 3, wherein the value n is an odd number larger than 3 and the elliptic reflecting surface is n 1/2th from the first transducer mounting side surface.

16. An ultrasonic delay line according to claim 4, wherein the value n is an odd number larger than 3 and the elliptic reflecting surface is n l/2th from the first transducer mounting side surface. 

1. An ultrasonic delay line comprising: a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and b. first and second electro-mechanical transducers for converting electrical energy into ultrasonic mechanical energy or vice versa, c. the solid plate having parallel, opposing first and second major surfaces, first and second transducer mounting side surfaces normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D1 to Dn (n being an integer) normal to the first and second major surfaces, d. i. the first electro-mechanical transducer being mounted on the first transducer mounting side surface and polarized parallel to the first and second major surfaces and the first mounting side surface, ii. the second electro-mechanical transducer being mounted on the second transducer mounting side surface and polarized parallel to the first and second major surfaces and the second mounting side surface, e. the first and second mounting side surfaces and the reflecting surfaces D1 to Dn being arranged relative to one other in such a manner that the ultrasonic wave, emitted from the first electro-mechanical transducer and normal to the central point on the first mounting side surface corresponding to the effective central point on the first electro-mechanical transducer viewed from the sides of the first and second major surfaces, propagates in the solid plate and is successively reflected at central points P1, P2, ... Pn on the reflecting surfaces D1, D2, ... Dn viewed from the sides of the first and second major surfaces and strikes the second electro-mechanical transducer normal to the second mounting side surface corresponding to the effective central point on the second electro-mechanical transducer, viewed from the sides of the first and second major surfaces, f. i. each of the reflecting surfaces Dl to Dn except one of them De lying in a plane extending along a straight line passing the central point on that reflecting surface viewed from the sides of the first and second major surfaces (in the case of n 1, any of such reflecting surfaces being not present), and ii. said reflecting surface De extending along a elliptic line whose focuses are effectively located at the central points on the first and second mounting side surfaces viewed from the central point of the elliptic reflecting surface De viewed from the sIdes of the first and second major surfaces or at equivalent central points to them and which passes the central point on the said elliptic reflecting surface De, to focus the ultrasonic wave from one transducer onto the other transducer.
 2. An ultrasonic delay line comprising: a. a solid plate propagation of ultrasonic mechanical energy therethrough, and b. an electro-mechanical transducer for converting electrical energy into ultrasonic mechanical energy or vice versa, c. the solid plate having parallel, opposing first and second major surfaces, a transducer mounting side surface normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D1 to Dn normal to the first and second major surfaces, d. the electro-mechanical transducer being mounted on the transducer mounting side surface and polarized parallel to the first and second major surfaces and the mounting side surface, e. the mounting side surface and the reflecting surfaces D1 to Dn being arranged relative to one other in such a manner that the ultrasonic wave, emitted from the first electro-mechanical transducer normal to the first mounting side surface corresponding to the effective central point on the electro-mechanical transducer viewed from the sides of the first and second major surfaces, propagates in the solid plate and is successively reflected at central points P1, P2, ... Pn on the reflecting surfaces D1, D2, ... Dn viewed from the sides of the first and second major surfaces and then successively reflected again at the central points Pn 1, Pn 2, ... P1 on the reflecting surfaces Dn 1, Dn 2, ... D1 and strike the electro-mechanical transducer, f. i. each of the reflecting surfaces D1 to Dn except one of them De lying in a plane extending along a straight line passing the central point on that reflecting surface viewed from the sides of the first and second major surfaces, and ii. said reflecting surface De extending along an elliptic line whose focuses are selected at the central points on the mounting side surface and reflecting surface Dn viewed from the central point on the reflecting surface De viewed from the sides of the first and second major surfaces or at equivalent central points to them and which passes the central point on the reflecting surface De.
 3. An ultrasonic delay line comprising: a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and b. first and second electro-mechanical transducers for converting electrical energy into ultrasonic mechanical energy or vice versa, c. the solid plate having parallel, opposing first and second major surfaces, first and second transducer mounting side surfaces normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D1 to Dn normal to the first and second major surfaces, d i. the first electro-mechanical transducer being mounted on the first transducer mounting side surface and polarized parallel to the first and second major surfaces and the first mounting side surface, ii. the second electro-mechanical transducer being mounted on the second transducer mounting side surface and polarized parallel to the first and second major surfaces and the second mounting side surface, e. the first and second mounting side surfaces and the reflecting surfaces D1 to Dn being arranged relative to one other in such a manner that the ultrasonic waves, emitted from the first electro-mechanical transducer normal to the central and first and second side points on thE first mounting side surface corresponding to the effective central and both side points on the first electro-mechanical transducer viewed from the sides of the first and second major surfaces, respectively propagate in the solid plate along paths of the same length and are successively reflected at central points P1, P2, ... Pn and first and second side points c1 and d1, c2 and d2, ... cn and dn on the both sides thereof on the reflecting surfaces D1, D2, ... Dn viewed from the sides of the first and second major surfaces and strike the second electro-mechanical transducer perpendicularly passing the central point and first and second side points on the second mounting side surface respectively corresponding to the effective central and both side points on the second electro-mechanical transducer, viewed from the sides of the first and second major surfaces, f. i. each of the reflecting surfaces D1 to Dn except one of them De lying in a plane extending along a straight line passing the central point on that reflecting surface viewed from the sides of the first and second major surface (in the case of n 1, any of such reflecting surfaces being not present), ii. said reflecting surface De comprising a linear surface area extending along a straight line connecting the first and second side points on the reflecting surface and first and second elliptic surface areas continuously extending outwardly of the linear surface area, viewed from the sides of the first and second major surfaces, iii. the first elliptic surface area extending along a first elliptic line whose focuses are at the first side points on the first and second mounting side surfaces viewed from the first side point on the linear surface area or their equivalent side poitns and which starts from the first side point on the linear surface area, and iv. the second elliptic surface area lying in a plane extending along a second elliptic line whose focuses are at the second side points on the first and second mounting side surfaces viewed from the second side point on the linear surface area or their equivalent side points and which starts from the second side point on the linear surface area.
 4. An ultrasonic delay line comprising: a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and b. an electro-mechanical transducer for converting electrical energy into ultrasonic mechanical energy or vice versa, c. the solid plate having parallel, opposing first and second major surfaces, a transducer mounting side surface normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D1 to Dn normal to the first and second major surfaces, d. the electro-mechanical transducer being mounted on the the transducer mounting side surface and polarized parallel to the first and second major surfaces and the mounting side surface, e. the mounting side surface and the reflecting surfaces D1 to Dn being arranged relative to one other in such a manner that the ultrasonic waves, emitted from the first electro-mechanical transducer normal to the central and first and second side points on the first mounting side surface respectively corresponding to the effective central and both side points on the electro-mechanical transducer viewed from the sides of the first and second major surfaces, respectively propagates in the solid plate along paths of the same length and are successively reflected at central points P1, P2, ... Pn and first and second side points c1 and d1, c2 and d2, ... cn and dn on the both sides thereof on the reflecting surfaces D1, D2, ... Dn vIewed from the sides of the first and second major surfaces and then successively reflected again at the central points Pn 1, Pn 2, ... P1 and the first and second side points cn 1 and dn 1, cn 2 and dn 2 ,... c1 and d1 respectively on the both sides thereof and strike the electro-mechanical transducer, f. i. each of the reflecting surfaces D1 to Dn except one of them lying in a plane extending along a straight line passing the central point on that reflecting surface viewed from the sides of the first and second major surfaces ii. the reflecting surface De comprising a linear surface area extending along a straight line connecting the first and second side points on the reflecting surfaces and first and second elliptic surface areas continuously extending outwardly of the linear surface area, viewed from the sides of the first and second major surfaces, iii. the first elliptic surface area extending along a first elliptic line whose focuses are at the first side points on the first and second mounting side surfaces viewed from the first side points on the linear surface area or their equivalent side points and which starts from the first side point on the linear surface area, and iv. the second elliptic surface area extending along a second elliptic line whose focuses are at the second side points on the first and second mounting side surfaces viewed from the second side point on the linear surface area or their equivalent side points and which starts from the second side point on the linear surface area.
 5. An ultrasonic delay line comprising: a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and b. first and second electro-mechanical transducers for converting electrical energy into ultrasonic mechanical energy or vice versa, c. the solid plate having parallel, opposing first and second major surfaces, first and second transducer mounting side surfaces normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D1 to Dn normal to the first and second major surfaces, d. i. the first electro-mechanical transducer being mounted on the first transducer mounting side surface and polarized parallel to the first and second major surfaces and the first mounting side surface, ii. the second electro-mechanical transducer being mounted on the second transducer mounting side surface and polarized parallel to the first and second major surfaces and the second mounting side surface, e. the first and second mounting side surfaces and the reflecting surfaces D1 to Dn being arranged relative to one other in such a manner that the ultrasonic wave, emitted from the first electro-mechanical transducer and normal to the central point on the first mounting side surface corresponding to the effective central point on the first electro-mechanical transducer viewed from the sides of the first and second major surfaces, propagates in the solid plate and is successively reflected at central points P1, P2, ... Pn on the reflecting surfaces D1, D2, ... Dn viewed from the sides of the first and second major surfaces and strikes the second electro-mechanical transducer perpendicularly passing the central point on the second mounting side surface corresponding to the effective central point on the second electro-mechanical transducer, viewed from the sides of the irst and second major surfaces, f. i. each of the reflecting surfaces except q reflecting surfaces De1, De2, ... Deq respectively sequentially selected from those D1 to Dn lying in a plane extending along a straight line passing the central point on that reflecting sUrface, viewed from the sides of the first and second major surfaces (in the case of n q, such linear reflecting surfaces are not present), ii. each of the reflecting surfaces De2, De4, ... De(q 1) lying in a plane extending along a straight line passing the central point on that reflecting surface, viewed from the sides of the first and second major surfaces, and iii. the reflecting surface De1 (i 1, 3, ... q), if the central point on the mounting side surface is taken as g0if the central points on the reflecting surfaces De1, De2, ... Deq are taken as g1, g2, ... gq respectively and if the central point on the second mounting side surface is taken as g(q 1), lying in a plane extending along an elliptic line whose focuses are at the central points gi 1 and gi 1 viewed from the central point gi viewed from the sides of the first and second major surfaces and which passes the central point gi.
 6. An ultrasonic delay line comprising: a. a solid plate for propagation of ultrasonic mechanical energy therethrough, and b. an electro-mechanical tranducer for converting electrical energy into ultrasonic mechanical energy or vice versa, c. the solid plate having parallel, opposing first and second major surfaces, a transducer mounting side surface normal to the first and second major surfaces and extending along a straight line when viewed from the sides of the first and second major surfaces, and n reflecting surfaces D1 to Dn normal to the first and second major surfaces, d. the electro-mechanical transducer being mounted on the transducer mounting side surface and polarized parallel to the first and second major surfaces and the mounting side surface, e. the mounting side surface and the reflecting surfaces D1 to Dn being arranged relative to one other in such a manner that the ultrasonic wave, emitted from the electro-mechanical transducer normal to the central point on the mounting side surface corresponding to the effective central point on the electro-mechanical transducer viewed from the sides of the first and second major surfaces, propagates in the solid plate and is successively reflected at central points P1, P2, ... Pn on the reflecting surfaces D1, D2, ... Dn viewed from the sides of the first and second major surfaces and then successively reflected again at the central points Pn 1, Pn 2, ... P1 on the reflecting surfaces Dn 1, Dn 2, ... D1 and strikes the electro-mechanical transducer, f. i. each of the reflecting surfaces except q reflecting surfaces (taken as De1, De2, ... Deq respectively sequentially selected from those D1 to Dn 1 lying in a plane extending along a straight line passing the central point on the reflecting surface, viewed from the sides of the first and second major surfaces, ii. each of the reflecting surfaces De2, De4, ... De(q 1) lying in a plane extending along a straight line passing the central point on that reflecting surface, viewed from the sides of the first and second major surfaces, and iii. the reflecting surface Dei (i 1, 3, ... q), if the central point on the mounting side surface is taken as g0, if the central points on the reflecting surfaces De1, De2, ... Deq are taken as g1, g2, ... gq respectively and if the central point Pn on the reflecting surface is taken as g(q 1), extending along an elliptic line whose focuses are at the central points gi 1 and gi 1 viewed from the central point gi viewed fRom the sides of the first and second major surfaces and which passes the central point gi.
 7. An ultrasonic delay line according to claim 1 wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.
 8. An ultrasonic delay line according to claim 2, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wave length of the ultrasonic mechanical energy wave.
 9. An ultrasonic delay line according to claim 3, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.
 10. An ultrasonic delay line according to claim 4, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.
 11. An ultrasonic delay line according to claim 5, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.
 12. An ultrasonic delay line according to claim 6, wherein the distance between the first and second major surfaces is 0.5 to 5 times the wavelength of the ultrasonic mechanical energy wave.
 13. An ultrasonic delay line according to claim 1 wherein the value n is an odd number larger than 3 and the elliptic reflecting surface is n + 1/2 th from the first transducer mounting side surface.
 14. An ultrasonic delay line according to claim 2, wherein the value n is an odd number larger than 3 and the elliptic reflecting surface is n + 1/2 th from the first transducer mounting side surface.
 15. An ultrasonic delay line according to claim 3, wherein the value n is an odd number larger than 3 and the elliptic reflecting surface is n + 1/2th from the first transducer mounting side surface.
 16. An ultrasonic delay line according to claim 4, wherein the value n is an odd number larger than 3 and the elliptic reflecting surface is n + 1/2th from the first transducer mounting side surface. 